Polydialkylsilanes have been investigated as optical and electronic functional materials used in precursors of silicon carbide materials, organic photoreceptors, optical waveguides, optical memory, or the like. Such polydialkylsilanes can be produced by subjecting dialkylhalosilanes to a reaction in the presence of an alkali metal. For example, in PTL 1, it is disclosed that polydimethylsilane is produced by melting or dispersing 1.05 moles of sodium metal in toluene, adding 0.5 moles of dimethyldichlorosilane dropwise to the dispersion over 8 hours (average addition rate=0.0625 moles·hr−1), and subjecting the mixture to a reaction at a toluene reflux temperature.